1. Field of the Invention
The present invention relates generally to power consumption control of a system, and more particularly to power consumption control of a system having a standby mode for saving power.
2. Description of the Related Art
FIG. 1 is a schematic block diagram illustrating a conventional power control apparatus. An overall system 100 of FIG. 1 includes a conventional power control apparatus which supplies power to a load 104 through a power supply unit 102. As shown in FIG. 1, in the overall system 100, the power supply unit 102 converts Alternating Current (AC) power into Direct Current (DC) power and provides the load 104 of the conventional system 100 with the DC power.
The power supply unit 102 is a Switching Mode Power Supply (SMPS) and normal AC power is input to the power supply unit 102. An output voltage level of the power supply unit 102 is controlled to 12 volts DC by operations of a zener diode 114, whose rated voltage is 12 volts, and a feedback control unit 110. Since the rated voltage of the zener diode 114 is 12 volts, a voltage is fed back to the control unit 110 if a voltage across the zener exceeds 12 volts. The feedback control unit 110 stops the operation of the power supply unit 102 if the output voltage of the power supply unit 102 is found to exceed 12 volts by observing the output voltage level.
A constant voltage unit 106 drops the 12 volts DC output from the power supply unit 102 to 5 volts DC, and provides a control unit 108 with the 5 volts DC. The 5 volts DC output from the constant voltage unit 106 is the operational voltage of the control unit 108. The constant voltage unit 106 is a kind of voltage regulator, and serves to obtain output voltage of a desired level by dissipating heat corresponding to a difference between an input voltage and a target output voltage, thus consuming the difference.
An AC power detection unit 112 observes whether normal AC power is input to the power supply unit 102, and provides the control unit 108 with observation results. The AC power detection unit 112 determines whether input AC power is normal by zero point detection of the AC power. Additionally, since the period of the AC power is constant, the motor rotation velocity and motor driving member of the load 104 and the like are precisely controllable by the zero point detection.
FIGS. 2A through 2D are waveform diagrams illustrating electrical characteristics of portions of the conventional system 100, that is, the voltage of nodes N1 through N4 as shown in FIG. 1. At node N1, the output voltage of the power supply unit 102 is always maintained at 12 volts as shown in FIG. 2A. At node N2, the output voltage of the constant voltage unit 106 is always maintained at 5 volts as shown in FIG. 2B. At node N3, AC power is input to the AC power detection unit 112 in a form of a wave as shown in FIG. 2C. At node N4, a pulse signal, as shown in FIG. 2D, generated within the power supply unit 102 determines a value of the output voltage at node N1.
In FIGS. 2A2D, ta and tb indicate a beginning of an operation stopping period and a beginning of an operation restarting period, respectively, of the system 100. The operation stopping period ta to tb of the system 100 designates an idle state in which the load 104 is not required to operate. In such an operation stopping period, the control unit 108 observes whether an external input occurs and whether the external input possesses data required for the operation of the system 100, so the control unit 108 must be activated. Upon receipt of the required data, the system 100 is restarted at time tb.
However, in accordance with the prior art, while the system 100 is not in operation, the voltage of 12 volts is continuously provided to the constant voltage unit 106 and AC power is continuously provided to the AC power detection unit 112. Accordingly, in the constant voltage unit 106, unnecessary power consumption occurs in the process of dropping the 12 volts to the 5 volts and a large amount of heat is generated, so the performance of the conventional system 100 is deteriorated. Additionally, unnecessary power consumption occurs in the AC power detection unit 112, further contributing to system inefficiency.